Generally, in electric-hybrid vehicles (e.g., gas or fuel cell) an electric motor may be provided to propel the vehicle. At least one rechargeable battery, together with either an internal combustion engine or fuel cell, may provide energy to the electric motor when the motor is employed to propel the vehicle. During extended operation, battery power may be depleted and may require charging. Although immobile charging processes are available, (i.e., coupling the battery to an electrical outlet), such processes typically require the user to discontinue use of the vehicle. Consequently, mobile charging processes are implemented to charge the battery during vehicle operation, such as for example by generating electricity via a fuel cell, via power from the internal combustion engine (e.g., using a generator), and/or via regenerative braking (by converting vehicle momentum into electrical energy). As the battery is charged and discharged, the state of charge may be regulated to extend battery life, optimize battery discharge and charge capacity, and ensure sufficient battery power for the electric motor.
The battery state of charge is typically regulated between a lower limit and an upper limit (i.e., a designated state of charge range) within which the battery state of charge may vary. If the state of charge breaches the upper limit (typically due to overcharging), recharging may be suspended until the battery can be discharged. Conversely, if the state of charge breaches the lower limit (typically due to lengthy electric motor operation), discharging (e.g., use of the electric motor) may be suspended until the battery can be charged. When the battery operates within the designated range, the state of charge is typically regulated to a target state of charge set to the midpoint of the designated range. This midpoint provides equal capacity to charge and discharge the battery, but cannot accommodate extended charging or discharging. Some systems and methods exist can continually regulate and vary the target state of charge based upon predicted vehicle driving conditions to optimize regenerative braking capacity. However, such systems have limited success due to the difficulty in determining and predicting upcoming road conditions. Moreover, such systems can add cost and weight to the vehicle. Accordingly, there is a need to improve the control of a battery state of charge.